GB2108660A

GB2108660A - Method for the rapid qualification of solid materials such as pozzolanas

Info

Publication number: GB2108660A
Application number: GB08228824A
Authority: GB
Inventors: Istvan Sajo; Gyorgy Vamos; Barbara Sipos; Miklos Urmossy; Eva Zemplen; Eva Borsovszky; Laszlo Barta
Original assignee: Vasipari Kutato Intezet; Energiagazdalkodasi Intezet
Current assignee: Vasipari Kutato Intezet; Energiagazdalkodasi Intezet
Priority date: 1981-10-14
Filing date: 1982-10-08
Publication date: 1983-05-18
Also published as: PL238596A1; GB2108660B; PL138639B1; FR2514509A1; SE8205753D0; SU1279539A1; US4491633A; DE3238142A1; SU1279539A3; CS247068B2; AT391557B; JPS58135442A; HU183622B; CH659325A5; DE3238142C2; SE461059B; FR2514509B1; DD210987A1; BE894700A; ATA370482A

Description

1 GB 2 108 660 A 1

SPECIFICATION

Method for the fast qualification of solid materials The invention relates to a new method for the 5 fast qualification of solid materials, mainly of pozzolanas. The aim of this qualification is to determine or predict the industrial usability of these materials.

It is very important in practice to determine in advance some substantial properties of basic industrial raw materials used for manufacturing some industrial products since in the knowledge of these properties one can determine the optimal conditions of manufacturing. For the most part these basic raw materials are minerals or other substances of mineral origin and great quantities of these materials with a great variety of chemical and physical properties are used in certain branches of the industry. For this preliminary qualification of basic raw materials there are always made efforts to disrupt the whole structure carrying chemical properties of the examined material according to the classic analytical methods while the methods without destruction are used for determination of physical properties in most instances.

However, very often such characteristics have to be determined in practical tasks which depend on both the chemical and physical properties of materials and the interaction of these properties can not be defined numerically at all or only by very complicated methods. So the actual properties which are characteristic of certain materials, e.g. the reactivity, can be only very laboriously and lengthily determined by conventional methods, primarily in the case of reactions between solid materials. Namely, the behaviour of a certain material is determined by many factors in a given reaction so not only by its chemical composition but inter alia by the specific 105 surface, the availability of its surface, the ratio between the crystalline and amorphous phases, the size and porosity of the particles, the moistening capacitv, etc. as well.

The above statements are especially true in the 110 case of the preliminary qualification of pozzolana and other substances of mineral origin or milling products and mixtures thereof. Namely, to determine such properties of these materials which are decisive from the point of view of their 115 industrial applicability is a typical task that can be solved by conventional methods only with great loss of time and under enormous difficulties. For example, the requirements raised of one of pozzolanas, i.e. fly ash, can be very different 120 depending on the field of utilization. On the basis of researches and experiences made so far it can be generally said that fly ashes of coarse particle size and of given moisture content are suitable for building a resistant bank whereas those of fine particle size and quite dry are best as concrete additives. But one of the most important characteristics of fly ashes for using them as concrete and mortar or other binding material additives is the so-called hydraulic activity. This expression means the very feature of fly ash that its soluble constituents are able to react with calcium hydroxide originating from the hydration of binding materials, e.g. concrete, or added into the system by another way and as a result of this reaction secondary hydrated phases, mostly calcium silicate hydrates, form. These materials are similar to hydrated products of concrete and responsible for the binding. The rate of these reactions depends to a great extent on the quality of reacting soluble constituents, i.e. it depends on the chemical composition of the material, the size of its specific surface and the ratio of vitreous phases, respectively.

So far, however, there is no standardized analytical method for such a qualification of fly ashes. As the hydraulic activity of fly ashes depends on their above-mentioned chemical and physical properties first of all the so-called lime adsorption method (described in a Soviet standard referred to in the present specification as GOST) is used for qualification in practice. But this means in practice that the qualification of a waste material, in the present case that of fly ash, can be carried out only after the time prescribed in this standard, i.e. after 28 days. One can rank the value of a fly ash as a pozzolana used in a subsequent production process only after this period. Even in the case of advantageous results of the above analysis one has to reckon with the fact that the physical properties of fly ash could undergo a complete change in comparison with its initial stage during the period of analysis or it could be mixed with other fly ashes of different quality in the course of its storage.

It is obvious from the foregoing that the known methods for the qualification of pozzolanas, have a great drawback in the sense that an opinion about their best usability can be only formed with a very great time-lag, i.e. after 28 days, in the practice. Moreover, these methods are rather ponderous as well and only the ability of lime adsorption of the material in question is determined essentially by a chemical analysis. According to the prior art, in our best knowledge, there is no more developed method than the above-mentioned one for the determination of the hydraulic activity of pozzolanas and for the qualification of these materials from the point of view of industrial usability.

Thus, the aim of the invention is to develop a method of qualification of the properties of pozzolanas through a fast, exact and numerical determination and thus making possible to evaluate the solid materials in question in a short time. With this qualification method it is intended to determine the very feature of certain materials, dusty products or milling products which is jointly typical of their chemical and physical properties.

By this means, on the one hand, we want to render possible the fast measurement of the suitability of certain materials for given technologies and, on the other hand, the qualifying control of pre- treating technologies 2 GB 2 108 660 A 2 comprising communication and grinding.

Our invention is based on the unexpected recognition that it is possible to define the pozzolana-property and activity of solid materials, primarily of pozzolanas, from the point of view of industrial usability by a single figure when in a system of constant heat capacity the material to be examined is brought together with fluoride ions in an acidic medium, whereafter during the reaction taking place in this system the change of heat quantity is measured and evaluated in the initial, preferably approximately linear, phase. The degree of the change of the heat quantity is measured in the initial, preferably approximately linear, phase of the reaction, most preferably within less than 30 seconds, e.g. at about the 20th second, and by converting the time function of the change of the heat quantity into a change of voltage; the rise of this latter curve is determined which is jointly characteristic of the above-mentioned chemical and physical properties of the material. According to a preferred embodiment of the present invention a usual computer attached to the above-described thermometric analyser system provides these measured and calculated data directly as mg of adsorbed CaO/g fly ash by using a constant programmed in advance in comparison to the lime adsorption by GOST. Naturally, the method of the invention can be performed also with graphic evaluation of the results obtained through the change of the heat quantity and measured by 95 thermometric way, i.e. by reckoning the rise of curve of the linear section and proportioning these data with a standard method, without the use of a previously programmed computer, although in such a manner this method becomes 100 slower and more difficult. (For the sake of caution we would remark that the type of the computer is by no means critical from the point of view of the present invention). It is possible to take into account longer or shorter periods of the change of 105 the heat quantity for the evaluation but in our opinion it is suitable to take a period of about 20 seconds in the case of Hungarian fly ashes because the determination of the activity and the qualification of the products seem to be the most 110 precise at about this moment. In any case, for the sake of authenticity it is favourable to carry out the measurement according to the method of the invention in the linear section of the time function of the change of the heat quantity.

The following examples are given for illustrating the method according to our invention without limiting, however, the scope of the invention.

Example 1

From an average sample of fly ash originating from the steam power station at P6cs (Hungary) a quantity of 3 g is added to 200.0 mi of a 5% aqueous hydrochloric acid solution under continuous stirring. The formed aqueous slurry is brought into the measuring cell of a thermometric titration apparatus. After thermostating during 5 minutes the slurry is titrated for 1 minute by adding 40% aqueous hydrogen fluoride solution in excess under continuous stirring. During this time the temperature change is determined and the increase of the heat quantity measured in the 20th second is determined by computer evaluation as an activity value. This value was 40 mg CaO/g fly ash.

By performing the titration of the same average sample of fly ash with an aqueous calcium hydroxide solution according to the GOST the lime adsorption value of the 28th day is 39 mg CaO/g fly ash after summarizing the values of each day.

After qualifying the fly ash according to the method of the invention it was used directly in a 1:4 mixture of lime and fly ash for byilding an agricultural road in the county Toina Hungary), where the contractor asked for the mixture of lime and fly ash as binding material in place of cement.

Because the fly ash could not be analysed by the standard method in due time, the fly ash was qualified by the method of the invention.

The fast use resulted in considerable saving in the building of a road of 2.1 km length.

Example 2

A possibility arose in relation to the fly ash originating from the steam power station Gagarin (county Heves, Hungary), that it can be added to a cement when its activity is greater than 70 mg CaQ/g fly ash. In this case it is not necessary to mill the fly ash and the cement together. So, at intervals of 30 minutes samples were taken from the fly ash continuously leaving the power station and these samples were measured and evaluated in the manner described in Example 1. As the preparation of the sample and the analysis took only some minutes and the calculation of the activity took only a few second, it was possible to take steps continuously that the fly ash could be gathered in a silo when its activity was greater than 70 mg CaO/g fly ash (with a permissible deviation of + 10%) and the fly ash could be directed to a slurry area when its activity was under this limit. So we succeeded in sending charges of fly ash into the silo with an average activity of fly ash of 94 mg CaO/g and this fly ash could be directly available for cement production. By doing so about 19 kWh of electric energy/t cement could be saved.

Afterwards making the titration by GOST from the average sample of gathered fly ash a 91 mg CaO/g value of lime adsorption activity for the 28th day could be measured.

The advantages of the method according to the present invention can be summarized as follows:

In a few minutes of sample-preparing and in a very short time, generally within less than 30 seconds, of analysis a measurement result, characterized only by a single figure for the pozzolana-activity of a material, is obtained which depends on the chemical and mineralogical composition as well as on the physical properties of this solid material, such as the specific surface, i 4 3 GB 2 108 660 A 3 the rate of crystalline and amorphous phases, the size of the particles, the porosity, the moistening capacity, etc., the analysed material can be qualified at once practically in the very moment of its formation, from the point of view how and in which ratio is it possible to use it as a raw material in a manufacturing process or for this purpose materials of the same activity can be gathered and stored together, in general, materials considered otherwise as a waste, e.g. fly ashes, become useful raw materials of exactly classified quality.

Claims

1. A method for the fast determination of activity and for the qualification of solid materials, e.g. pozzolanas, from the point of view of industrial usability comprising the steps of 40 bringing together said materials with fluoride ions in an acidic medium in a system of constant heat capacity, measuring and evaluating the change of the heat quantity in the initial, preferably approximately linear, phase of the reaction occurring in said system.

2. A method as claimed in claim 1, wherein the time function of the change of the heat quantity in said system is converted into a change of voltage and the rise of the thus-obtained curve is determined, suitably in the linear phase of said curve.

3. A method as claimed in claim 1 or 2, wherein the value of the change of heat quantity of said system is determined during the initial phase of the reaction, suitably within less than 30 seconds, favourably at about the 20th second.

4. A method as claimed in any one of claims 1 to 3, wherein the measured result of the change of the heat quantity is evaluated by using constant value being characteristic of said solid material and programmed in a computer.

5. A method according to claim 1 substantially as herein described in either of the Examples.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained